The 2.5-liter M20B25 engine does not have a catalytic converter. When it was first introduced, it had a carburetor; later, Bosch added a fuel injection system. Bosch Motronic 1.1/1.3 was the engine management system. The capacity was raised after the B25 was upgraded in 1987.
A catalyzed model with Motronic 1.3 engine management debuted in 1987. Although the compression ratio was lowered to 8.8:1, the power remained almost unchanged at 125 kW (170 PS; 168 hp) because of the more advanced electronics. For markets in Southern Europe and other regions where unleaded gasoline was not consistently accessible, the uncatalyzed engine was kept in production.
Specifications
| Manufacturer | Munich Plant |
| Family | M20 |
| Production years | 1986-1993 |
| Cylinder block alloy | cast iron |
| Fuel system | injector |
| Configuration | inline |
| Number of cylinders | 6 |
| Valves per cylinder | 2 |
| Piston stroke, mm | 75 |
| Cylinder bore, mm | 84 |
| Compression ratio | 9.7 9.7 8.8 |
| Displacement, cc | 2494 |
| Power output, hp | 163/5800 171/5800 170/5800 |
| Torque output, Nm / rpm | 215/4000 226/4000 222/4300 |
| Fuel type | petrol |
| Weight, kg | ~117 (dry) |
| Fuel consumption, L/100 km (for E30 325i) — city — highway — combined |
12.9 7.2 9.0 |
| Oil consumption, gr/1000 km | up to 1000 |
| Recommended engine oil | 5W-30 / 5W-40 / 10W-30 / 10W-40 / 10W-50 / 15W-40 / 15W-50 |
| Engine oil capacity, liter | 4.75 |
| Normal engine operating temperature, °C | ~90 |
| Engine lifespan, km | ~300 000 |
Frequent problems
Ttemperature increase. The cylinder head overheats and results from a cooling system malfunction. Examine the radiator’s overall health, the thermostat, the pump, and any air obstructions.
Worn-out camshaft pastels. The camshaft knocking after more than 200,000 kilometers is a distinctive feature. Repair: a new cylinder head is installed.
There is a crack in the cylinder head. M20 is a typical illness. Overheating is the cause. The fourth and fifth cylinders are typically where the crack appears. It is necessary to replace the cylinder head.
A comprehensive inspection is also required for the M20B25 unit’s tensioner roller and timing belt. It is impossible to prevent valve bends and occasionally even the total destruction of the pistons if the belt breaks. The engines in this series display typical aging defects as they age (keep in mind that they have been manufactured since 1986). Because of this, purchasing a car with this unit is not a very promising endeavor in terms of its trouble-free future maintenance.